Arc furnace control system



Feb. 16, 1954 R. A. GEISELMAN ET AL ARC FURNACE CONTROL SYSTEM Filed Jan. 27, 1953 Proiecflve o4 Device i WITNESSES:

INVENTORS Patented Feb. 16, 1954 UNITED STATES PATENT OFFICE burgh, Pa assignors. to Westinghouse. Electric Corporation; EastPittsliurgh, Pa.-, a corporation;

of Pennsylvania Applicationi-la-nuary fl, 1953;. Serial1No. 333,458

4 Claims.

' invention relatesto control systems. and; Particularly, to control systemsfor governing the. operation of movableelectrodesof electric arc. furnaces,

' Whenthe movable. electrodes of. an. arc. fur, 5 nace, are; operated in close. proximity to. the. molten; bath as, normall the. case, certain. undesirable, featuresresult, For instance, if the. electrodescomeln. contact ,with. the molten bath. the. material of, the; electrodes, contaminate the, bath... This, can. even occur after the .powerto the. electrodes is, discontinued, since, the level of themoltenibath .continuesto. rise. dueto. further. meltmg. of the. charge. contained} therein, Fur: ther, lf-thevelectrodesremain.in contact with the, molten; bath, for a .sufiicient, time. to. allow. the: cooling of the bath, the movable electrodesmay freeze to thebath...

Inanw are. furnace syst m the. m vablelecrodes are. normally connected 1 to. the source, of power supp y throu h, a. circuit breaker. This; rcuit; breaker. durin th operation of. the are. furnace may be. int rrupt d a plur lity of times. during each hour of operation. Each timev the circuit breaker is interrupted the operator often ectuates the circuit breaker to,theclosedposition" under 1o ad,,tha,t is, when either-the sourceoij power. is. normally. supplying energy to the. moyable electro.des,, or; when a short circuit conditionexists. Theactuation of the ,circuit'break'er to theclosedposition under. load a. plurality of; times. each. hour shortens the. life. of a the circuit. breaker. considerably.

An object. ofthisinvention is to provide for, actuating anlelectrodeof an arcfurnacea prev determined, distance from its assmiatedmoltenbath oncethe main power supply to. theelsotrone,

been interrupted to. thereby prevent both contamination of, the moltenbathby the 618%." trode and freezing oithe. electrode in the ,molten. bfath,.by rendering acontrolrelay and timing, means responsive, to. the. circuit interruption. of, the. power. supply to, the. electrode, so, that the. control relay. initiates the movementof electrode, away from. the molten bath and the timingmeansstops such movement after a. predetermined time.

. Another. object .of this invention is .to provide for lengthening the life .ofvoircuit, interruptingmeans, connected. between a. movable, electrode of. anercfurnaceandits source. of power, by moving the electrode. apredetermined, distance, from the. molten bath, when the flow of "current is interrupted, sothat the, circuit interrupting means. is; not... closedwunder. load when... initiating;

an arc furnace operation.

Other ,objectsof this invention will becomeape parentfrom the following description wloentakenz conjunction withthe accompanying drawing, in which the singleiigure is aschematicdiagram. oLcircuitsand apparatus illustrating an embodie mentof the teachings of this. invention.

Referring to -.-the drawing there is illustrated/an arc furnace! 0, .comprising acontainer I 2, having; disposed therein .amoltenbath .l .4. As. illustrated; apluralityof movable. electrodes 16;,18 andlO; aredisposedin closeproximityto the uppersur; face of thezmolten bath, 14; In this instance. themovable electrodes. I .6, 1 Sand 20. are .directly connected to load conductors22; 241 and 26,.re; spectively, which .inturn are connected. to a suit, able source ofpowersupply (not shown) through circuit interruptingmeans 30'. Ailexible cable. 32. is ,connected..to the, movable electrodejll" and. is disposed, around a. suitable pulley 34. so as: to. raise andlowerthemovable electrode 2.0 in accordance. with, p edetermined; conditions which will. be explained hereinafter. The movable electrodes, I 6 and I8 also. hare associated; therewith fi'exiblecablesfli and 38 resp ctively, and pulleys, 40; and, 42; respectively.

Since the, operating mechanism for. each of'the three. phases supplying, the arcfurnace. I0, is, identical; the. operating mechanism for, only one phase isillustrated'in detail and is shown en.- closedin the rectangular area 46'; Ascan be'seen, from. the drawinswthe operating mechanism enclosed" within the; rectangular area 46' is, ESSO-r ciatedkwith the movable. electrode 20'. Ihe corresppnding operating mechanism fertile-movable electrodes [6' and. i8 is disposed'lwithin the-rec: tang ular areas- 48 and 50; respectively.

Referring; more particularly to the operating, mechanism within the rectangulararea- 46', theflexible 033318732 maybe wound upon a winding drumi5-2; operated bya reversible electrodemotor 5!. The motor 5'4 comprises a field winding' 56 disposed to' berenergized from any suitable direct? current: source, such. asthe battery 58; andan. armature-winding 60" connected byconductorstl" and' 64' to-be. suppliedwith energy from a main; enerator 56" that is drivenby analternating; current" motor 68. and excited by an exciter generator. mi

The mainenerator Eticomprises an armature. winding]! connected, to the. conductors 82v and Glyandga, field winding "disposed to be supplied with energy from-the armature winding. 'lfi' of the exciter generator through, a, seli-excitingfield windingjfl; Inthisinstance the motor fili receives alternating current energy from line conductors 8| and BI, which in turn are connected to a suitable source of alternating current power (not shown).

As illustrated, the exciter generator I6 is also provided with two control field windings 82 and 84, which are disposed to be so energized as to oppose each other and to cooperate in controlling the excitatiori of the cxciter generator iii. In order to render the control winding 84 of the exciter generator Hi responsive to the arc voltage of the movable electrode 20, one of the input terminals of a full-wave rectifier 88 is connected to the container i2 and the other input terminal of the rectifier 88 is connected to the movable electrode 20 through an adjustable resistor 90, the function or which will be described hereinafter. As illustrated the output terminals of the rectifier 83 are connected to the control field winding 8 of the exciter generator Ill.

On the other hand, in order to obtain a measure of the current fiow through the movable electrode 26, a current transformer 92 is disposed in inductive relationship with the load conductor 25. As can be seen from the drawing, the current transformer 92 is connected to the input terminals of a full-wave rectifier 94, through normally closed contact members $56 of a control relay 98, the function of which will be described hereinafter. In order to render the control field windingSZ responsive to the arc current of the movable electrode 20, the output terminals of the rectifier 9d are connected to the control field winding 82.v In this instance an adjustable resistor Illll is connected across the currenttransformer 92, which adjustable resistor in conjunction with the adjustable resistor 9%) provide the necessary adjustments for obtaining a balance between the control field windings 82 and 3d of the exciter generator 79, when the movable electrode'Zil is disposed a proper distance from the molten bath Id for operating conditions.

During the normal operation of the arc furnace'Il) the movable electrode 20 is maintained in a substantially constant regulated position relative to the molten bath I l. When so positioned the control field windings 32 and as have an equal and opposite efiect and thus the effects neutralize each other. However, if the movable electrode 25 moves closer to the molten bath ld' than its regulated position, the current fiow through the load conductor 26'increases tothereby increase the output of the current transformer 92, which in' turn increases the current flow through the control field winding 82. On the other hand, the lowering of the movable electrode 20 below its regulated position decreases the arc voltage as applied to the control field winding 84' through the rectifier 88. Thus, when the rnov-v able electrode 26 is located below its regulated position, the flux produced by the field winding 82 is greater in magnitude than the flux produced by the field winding 84. When the fiux produced by the field winding 82 is greater in magnitude than the flux produced by the field winding 84, the resultant flux will cause'the exciter generator l0 todevelop a voltage of such polarity as to energize the main generator field winding 74 in a direction to impress a voltage on the motor armature 60, having a polarity to cause the motor 54 to operate in a direction to raise the movable electrode 2!), to thereby return it to its regulated position. However, if, the flux produced by the control field winding E i. is greater in magnitude than the fiux produced by the control field winding 82, due to the fact that the movable electrode 20 is above its regulated position, the resultant fiux produced by the control field windings 82 and 84 will effect a lowering of the movable electrode 20, to thereby return it to its regulated position.

As hereinbefore mentioned, circuit interrupting means 30 is connected between the movable electrodes I6, I8 and 20 and their source of power supply (not shown). In this instance, the circuit interrupting means 39 comprises a trip device I02, which can either be manually energized by a pushbutton I04, or energized in response to a short circuit condition, to thereby trip the circuit interrupting means 30, and thus disconnect the movable electrodes I5, I8 and 20 from their source of power (not shown). In particular, a protective device I06 is disposed to be responsive to the outputs of current transformers I08, III) and I I2, which are disposed in inductive relationship with the load conductors 22, 24 and 28, respectively. In order to render the trip device I02 responsive to the output currents of the current transformers I08, IiIl and H2, normally open contact members I II) are disposed to be actuated in response to these output currents of the current transformers I08, III], and II2. A circuit for energizing the trip device I02 extends from a negative terminal I22 of a suitable direct current source (not shown) through the normally open contact members IIS of the protective device I05, an energizing winding II8 of the trip device I92, and auxiliary contact members I20 of the circuit interrupting means 30, to a positive terminal IE3 or the source of direct current (not shown). The circuit interrupting means 30 also controls auxiliary contact members I24 and I25, the function of which will be described here inafter.

In accordance with the teachings of this invention, in order to initiate the actuation of the movable electrode 20 in a direction away from the molten bath I4 once the. circuit interrupting means 38 has been actuated to the circuit interrupting position, the control relay 9B is provided. In this instance, the control relay 98 comprises the normally closed contacts and normally open contacts I30, associated with the operating mechanism disposed within the rectangular area 46. The control relay 9!) also comprises a corresponding set of contact members I3I and I32 associated with the operating mechanism disposed within the rectangular area 50,

and a corresponding set of contact membersIM' and I36 associated with the operating mechanism disposed within the rectangular area 48. In order to actuate the normally open contact members I39, I32 and I36 to the closed position, an operating coil I48 of the relay 98 is provided.

For the purpose or deenergizing the operating coil I40 of the control relay 98 once the movable electrode 20 has been raised a predetermined distance above its regulated position so that the material of the electrode 23 cannot contaminate the molten bath Id and cannot become frozen thereto, a time delay I42 is provided: In this instance, the time delay relay M2 comprises an When this occurs, a direct-current circuit is come pletedito; the; operating coil I40 of; then-controli relay; 98,", which circuit, extends fronra positiviterminahlliaofa direct current source ;of energy,

throughgthe operating coil Milofthe relay the-contact members lzfiof the circuit interrupt:

the, contact members Me of the-relay iii, andi taotmembers I 3d,. I 32 and, I 35 are actuated tothe:

closed-position; andthe normally closed-contact, members 95; are actuated to thezopen position; by the relay; 98- to thereby disconnect the current transformer 92 from the input terminals of the, rectifier; 9.4. By closing the i contact members I 35 oithe relay; 98 alternating current is supplied to; thezinputterminals of the rectifier 94throughxa.

potential transformer I 3 whose, secondary; windingfiiIB-Zis connectedacrossthe input terminals o s'therecetifier t4, when the contact members I30 are closed. However, since the contactmember 96 of the relay S5 is now in'the open position energy; is not consumed in passing current from the secondary winding; i 62 of the transformer tail to the current transformer 92 and. variable resistor I00.

With the secondary winding I62 of the transformer I69 connected to the input terminals of the rectifier 94, the current flow through the control field winding 52 of the exciter generator ii) is such as to effect a raising of the movable elec-- trode above its regulated position, which move ment takes place until the action of the time delay relay I42 stops such movement.

In particular, when the circuit interrupting means is tripped open, the auxiliary contact members I24 of the circuit interrupting means 30 are actuated to the closed position, thereby completing an alternating current circuit to the operating coil I44 of the time delay relay I42. After a predetermined time, as determined by the setting of the time delay relay M2, the normally closed contact members I48 of the time delay relay I42 are actuated to the open position, thereby interrupting the direct-current circuit to the operating coil Mt of the control relay $39. The deenergizing of the operating coil I48 causes the normally open contact members I38, I32 and I36 to be actuated to their open position. By actuating the contact members I30, I32 and I to the open position, the circuit from the secondary winding I62 of the transformer [St to the input terminals of the rectifier S4 is interrupted, to thereby deenergize the control field winding 82 of the exciter generator 19, and thus stop the movement of the movable electrode 23. It is to be noted that the control field windings 82 and 8- 2 or" the exciter generator Iii do not receive current from the current transformer 92, or from the eiiect of the voltage beteen the movable electode 2c and the container I2, since both the arc current and are voltage are zero when the circuit interrupting means is in the open position.

In order to reclose the circuit interrupting means 30 and restore the system to its normal operating condition, a pushbutton IE6 is disposed to be actuated to thereby complete an energizing circuit to an energizing winding I58 associated with the circuit interrupting means 38.

The apparatus embodying the teachings of this invention has several advantages. For instance, the length of life of the circuit interrupting means 30 is greatly increased. Further, the material of the movable electrodes I6, I8 and 20 cannot ipossibly contaminateithesmolten: bath; a oncerthezcircuit interrupting-means 30;. actu-y ated:tovthezopenzposition. Inaddition bypracr ticing this invention the movable 4 electrodes I 5&1, l8, and Zilcannot: freeze to themolten; bath; Ms, once ithasicooled sufiiciently, v

Sinceocertainr changes may be. madev in the; above2apparatusandpcircuits,. and? different emsbodiments of this; invention may bemadewithsout departingfrom the spirit and scope-thereof; it is: intended that'all' the. matter. contained in, the above description; or; shown in:the accom.-:-- panyingydra-wing shall .be; interpreted as; illuse trativ and-notinalimiting sense. I

W e claim as our invention:

1.: .In: an-arc furnace control system: for: controlling; the: positioning. of: a, movable electrode: with respectzto a, molten bath in which the are: receives: energy. from 2a "source-of power; 1311852160111! bination comprising, circuit interrupting means: connectedvbctween the source of'power andthe movable electrode, a ,motorgfor moving: the;elec=- trode iwitlrrespect to the molten bath,1control: means including a control relay responsivertoathe:

' opening ofthexcircuit interrupting means for so;

energizing the; motor: as to; actuate; the movable: electrode in a direction away from the molten bath whereby the material of the electrode cannot contaminate the molten bath, and timing means also responsive to the opening of the circuit interrupting means for deenergizing the control relay once the motor has actuated the movable electrode a predetermined distance from the molten bath to thereby stop the movement of the movable electrode.

2. In an arc furnace control system for controlling the positioning of a movable electrode with respect to a molten bath in which the arc receives energy from a source of power, the combination comprising, circuit interrupting means connected between the source of power and the movable electrode, a motor for moving the movable electrode with respect to the molten bath, means responsive to the current flow through the movable electrode for actuating the circuit interrupting means to the open position, control means including a control relay responsive to the opening of the circuit interrupting means for so energizing the motor as to actuate the movable electrode in a direction away from the molten bath whereby the material of the electrode cannot contaminate the molten bath, and a time delay relay also responsive to the opening of the circuit interrupting means for deenergizing the control relay once the motor has actuated the movable electrode a predetermined distance from the molten bath to thereby stop the movement of the movable electrode.

3. In an arc furnace control system for controlling the positioning of a movable electrode with respect to a molten bath in which the arc receives energy from a source of power, the combination comprising, circuit interrupting means connected between the source of power and the movable electrode, a motor for moving the electrode with respect to the molten bath, a generator for supplying power to the motor, a control winding for the generator, a full-wave rectifier having input and output terminals, the output terminals being connected to the control winding, a source of alternating current, circuit means including a control relay for connecting the source of alternating current to the input terminals of the rectifier; the control relay being responsive to the opening of the circuit interrupting means to thereby connect the source of alternating current to the input terminals of the rectifier to thus so energize the motor as to actuate the movable elecrode in a direction away from the molten bath whereby the material of the movable electrode cannot contaminate the molten bath, and a timedelay relay also responsive to the opening ofthe circuit interrupting means for deenergizing the control relay once a predetermined distance has been established between the movable electrode and the molten bath to thereby interrupt the circuit between the source of alternating-current and the input terminal of the rectifier to thereby stop the movement of the movable electrode.

4. In an arc fmnace control system for controlling the positioning o'f a movable electrode with respect to a molten bath in which the arc receives energy from a source of power, the combination' comprising, circuit interrupting means connected between the source of power and the movable electrode, a motor for moving the electrode with respect to the molten bath, a generator for supplying power to the motor, a control winding for the generator, a full-wave rectifier having input and output terminals, the output termi- 8 nals being connected to the control Winding, a source of alternating current, circuit means including a control relay for connecting the source of alternating-current to the input terminals of the rectifier, manual trip means for actuating the circuit interrupting mean to the open position, the control relay being responsive to the opening of the circuit interrupting means to thereby connect the source of alternating current to the input terminals of the rectifier to thus so energize the motor as to actuate the movable electrode in a direction away from the molten bath whereby the material of the movable electrode cannot contaminate the molten bath, and timing means also responsive to the opening of the circuit interrupting means for deenergizing the control relay once a predetermined distance has been established between the movable electrode and the molten bath to thereby interrupt the circuit between the source of alternating current and the input terminals of the rectifier to thereby stop the movement of the movable electrode.

RALPH A. GEISELMAN. GLENN C. BIGGS.

No references cited. 

